It is sometimes desirable to fabricate a bladed device by joining one or more separable blades to a hub. This is often the case in turbomachines such as propellers, rotary fans, compressors, turbines, or pumps which utilize rotating bladed devices to respectively impart or extract energy to or from a flow of fluid passing through the bladed device.
In some instances the bladed devices of turbomachines incorporate complex shapes which preclude their economical production as a single piece. Specifically, tooling costs and procedures or scrap rates may be so high that manufacture of the bladed device as a single unitary part is not practical.
In other instances, it is desirable to have a single turbomachine be capable of operating alternatively in a variety of installations requiring different performance characteristics from the turbomachine. By making the blades separable, a family of turbomachines may conveniently be provided to meet the requirements of various installations by simply changing the number or the configuration of the blades to provide a flow rate or pressure differential through the bladed device that is closely matched to the particular installation. With such an approach, the elements of the turbomachine other than the blades, such as drive motors, gear trains, housings, and the hub of the bladed device, may be common to all members of the family of turbomachines. Such commonality of elements offers significant manufacturing economy, thereby leading to reduced inventory levels and cost.
Another advantage of having separable blades is the ability to individually remove and replace damaged blades, or a damaged hub, thus precluding the need for the additional cost of replacing the entire bladed device. It is also desirable in some instances to utilize separable blades having similar fluid reacting configurations, but differing dynamic moments of inertia for balancing the bladed device without resorting to traditional methods of removing or adding material to the hub solely for the purpose of balancing.
Some prior attempts to provide a bladed device as described above have required the use of adhesives, fasteners, welding, or other retention means in addition to the blades and hub themselves for retaining and positioning the blades in the hub. Such approaches are illustrated in U.S. Pat. Nos. 5,354,177 to Chang, and U.S. Pat. No. 3,071,195 to Osmaston. The use of such additional retention means adds undesirable complexity and cost. It is therefore desirable to incorporate any installation and retention means required for joining the blades to the hub as integral features of the blades and the hub.
Other prior attempts, such as that illustrated by U.S. Pat. No. 3,952,712 to Hermansen have attempted to join a blade or blades to a hub or other rotating assembly using snap-on interlocking engagement tangs, or tongues. Unfortunately these tangs are sometimes configured such that centrifugally generated forces on the tangs while the bladed device is rotating tend to act in a manner leading to disengagement of the tangs, rather than self-energizing the tangs into tighter engagement.
Accordingly, it is an object of our invention to provide a bladed device having one or more blades attached to a hub that is rotatable about an axis in a self-locking manner providing retention of the blades to the hub against axially and radially directed forces acting on the blades with respect to the hub. Other objects of our invention include providing:
1) a bladed device as above in which the means for installing and retaining the blades in the hub are integrally formed as part of the blades and hub, thereby eliminating the need for any additional retention or installation means; PA1 2) a bladed device in which the shape or number of blades attached to a given hub can be conveniently changed to alter the performance of the bladed device or a turbomachine incorporating the bladed device; PA1 3) a bladed device having elements which are readily and economically manufacturable by a variety of processes including injection molding; PA1 4) a method of conveniently producing or readily repairing bladed devices having complex geometries; and
5) a bladed device as above wherein the blades and hub are configured to include integral snap action, self-energizing, and self-locking features for inserting and retaining the blades in the hub.